Atmospheric air surrounds both lands and oceans of the planet Earth. It is free, widely available, and acts as a main raw material for the air separation industries. In the 18^th century, Joseph Priestley, Antoine Lavoisier, and Henry Cavendish conducted the first atmospheric air composition measurement. According to NASA, the dry atmospheric air composition is as follows:

The compositions listed above are on a volumetric basis. They are essentially constant up to an altitude of 10,000 meters. Due to human activities, the carbon dioxide and methane compositions will keep increasing yearly. Currently, the Earth’s atmospheric air composition is measured using observations, laboratory studies, and computational modeling.

Source:

The Atmosphere: Getting a handle on carbon dioxide – NASA Science. (n.d.). https://science.nasa.gov/earth/climate-change/greenhouse-gases/the-atmosphere-getting-a-handle-on-carbon-dioxide/#hds-sidebar-nav-2